Viscous torsional vibration dampers provide a housing defining an axially opening annular working chamber. A complementary annular inertia mass ring is disposed inside the working chamber defined in the housing. A cover is sealed across the axial opening of the housing for confining the inertia ring within the annular working chamber. Opposed surfaces of the inertia ring and the housing are in shear film, spaced relation and a viscous damping fluid substantially fills the spaces between the inner walls of the housing and the inertia ring. A hub may be attached to the viscous torsional vibration damper for connecting the damper to a crankshaft. The cover that seals across the annular, axial opening of the housing may be attached to the housing by welding or it may be bolted onto the housing. Both of these methods of forming the torsional damper have drawbacks. Welding creates a permanent attachment of the cover to the housing and prevents disassembly and rebuilding without destruction. Welding may introduce thermal distortion. Also, welding requires the use of similar materials for the housing and the cover. Attaching the cover by means of threaded fasteners requires thicker materials which runs counter to the goal to reduce weight in high performance applications.